The effects of increased unsaturation in the sn-2 fatty acyl chain of phosphatidylcholines (PCs) on the lipid lateral diffusion have been investigated by pulsed-field gradient NMR. Macroscopically oriented bilayers containing a monosaturated PC, egg sphingomyelin, and cholesterol (CHOL) have been studied at temperatures between 0 degrees C and 60 degrees C, and the number of double bonds in the PC was one, two, four, or six. For PC bilayers, with and without the incorporation of egg sphingomyelin and CHOL, the lateral diffusion increased with increasing number of double bonds, as a consequence of the increased headgroup area caused by the unsaturation. Addition of CHOL caused a decrease in lipid diffusion due to the condensing effect of CHOL on the headgroup area. Phase separation into large domains of liquid-disordered and liquid-ordered phases were observed in the ternary systems with PCs containing four and six double bonds, as evidenced by the occurrence of two lipid diffusion coefficients. PC bilayers with one or two double bonds appear homogeneous on the length scales probed by the experiment, but the temperature dependence of the diffusion suggests that small domains may be present also in these ternary systems. 相似文献
Bacterial drug resistance is a serious concern for human health. Multidrug efflux pumps export a broad variety of substrates out of the cell and thereby convey resistance to the host. In Escherichia coli, the AcrB:AcrA:TolC efflux complex forms a principal transporter for which structures of the individual component proteins have been determined in isolation. Here, we present the X-ray structure of AcrB in complex with a single transmembrane protein, assigned by mass spectrometry as YajC. A specific rotation of the periplasmic porter domain of AcrB is also revealed, consistent with the hypothesized "twist-to-open" mechanism for TolC activation. Growth experiments with yajc-deleted E. coli reveal a modest increase in the organism's susceptibility to beta-lactam antibiotics, but this effect could not conclusively be attributed to the loss of interactions between YajC and AcrB. 相似文献
A type of biodegradable microsphere (DSM), approximately 45 microns in diameter, made of polymerized potato starch (Pharmacia, Sweden) was intravenously injected into rats to observe the state of DSM in small blood vessels in the kidney and liver at the electron microscopic level. Prior to their digestion with amylase, individual DSM changed their round shape to an irregularly folded one to occupy almost the whole area of the lumen. At the transmission electron microscopic level, DSM were impregnated with colloidal iron and were easily identified. Interaction of the iron labelled DSM with the surface of endothelial cells was unexpectedly loose and no adherence or fusion of this surface was observed. The starch substance was not visible in the pinocytotic vesicles of the endothelium. These findings suggest the independent profile of DSM in situ. 相似文献
Cell-penetrating peptides, CPPs, are used as delivery vectors for pharmacologically interesting substances, such as antisense
oligonucleotides, proteins and peptides. We present a general principle for designing cell-penetrating peptides derived from
naturally occurring proteins as well as from randomly generated polyamino acid sequences. Thereby, we introduce a novel pharmacological
principle for identification of cell-penetrating peptides for which the applications can be numerous, including cellular transduction
vectors and mimics of intracellular protein–protein interactions. The methods of identifying a CPP comprises assessing the
averaged bulk property values of the defined sequence, and ensuring that they fall within the bulk property value interval
obtained from the training set. Despite this simplistic approach, the search criteria proved useful for finding CPP properties
in either proteins or random sequences. We have experimentally verified cell-penetrating properties of 10–20-mer peptides
derived from naturally occurring proteins as well as from random poly-amino acids. We note that since CPPs can be found in
part of the protein sequences that may govern protein interactions, it is possible to produce cell-penetrating protein agonists
or antagonists. 相似文献
Unveiling the determinants for transferase and hydrolase activity in glycoside hydrolases would allow using their vast diversity for creating novel transglycosylases, thereby unlocking an extensive toolbox for carbohydrate chemists. Three different amino acid substitutions at position 220 of a GH1 β-glucosidase from Thermotoga neapolitana caused an increase of the ratio of transglycosylation to hydrolysis (rs/rh) from 0.33 to 1.45–2.71. Further increase in rs/rh was achieved by modulation of pH of the reaction medium. The wild-type enzyme had a pH optimum for both hydrolysis and transglycosylation around 6 and reduced activity at higher pH. Interestingly, the mutants had constant transglycosylation activity over a broad pH range (5–10), while the hydrolytic activity was largely eliminated at pH 10. The results demonstrate that a combination of protein engineering and medium engineering can be used to eliminate the hydrolytic activity without affecting the transglycosylation activity of a glycoside hydrolase. The underlying factors for this success are pursued, and perturbations of the catalytic acid/base in combination with flexibility are shown to be important factors.